The invention relates to a method of generating a control signal, in which method the control signal is generated from a digital signal which is converted into an analog control signal in a D/A converter.
In a prior art arrangement, the control signal of a means controlled by an analog control signal is typically generated by converting the digital signal into an analog control signal. Should the means be for example a voltage-controlled oscillator, the oscillator is controlled by an analog signal generated in a commercially available D/A converter. The D/A converter is coupled to a specific voltage reference, whereby the control voltage of the voltage-controlled means is rendered independent of variations in the operating voltage of the arrangement.
However, the prior art arrangement cannot be integrated as such into a digital ASIC circuit, for example. If the above arrangement is integrated into an ASIC circuit, the operating voltage of the D/A converter could change under the influence of e.g. the load on the arrangement and the temperature. If the operating voltage of a D/A converter changes, the change may also cause a change in the magnitude of the control signal, and consequently the arrangement would not operate in the desired manner. In practice this means that the voltage-controlled oscillator does not provide the desired frequency, but the actual frequency differs from the desired frequency to some degree.
It is therefore an object of the invention to provide a method and an apparatus implementing the method so as to solve the above problems. This is achieved by a method of the type described in the introduction and characterized by measuring the operating voltage of the D/A converter, and, when the operating voltage differs from a nominal value preset for the operating voltage of the D/A converter, changing the control signal on the basis of the measurement result obtained from the measurement of the operating voltage of the D/A converter.
The invention also relates to an arrangement comprising a D/A converter for receiving a digital signal and converting the received signal into an analog control signal.
The arrangement of the invention is characterized by comprising a measuring means for measuring the operating voltage of the D/A converter, a means for generating a difference signal from the measurement result obtained from the measurement of the operating voltage, and the nominal value of the operating voltage, the difference signal being used to change the control signal when the operating voltage differs from a nominal value preset for the operating voltage of the D/A converter.
The preferred embodiments of the invention are disclosed in the dependent claims.
The invention is based on taking into account the operating voltage of the D/A converter in the generation of the control signal, whereby a deviation of the operating voltage from the nominal value does not affect the control signal to be generated.
The method and arrangement of the invention provide a plurality of advantages. The arrangement takes into account variations in the operating voltage during generation of the control signal, whereby the control signal is always optimal in size. A control signal thus generated ensures that the means to be controlled operates in the desired manner. The method of the invention is particularly efficient in compensating for slow variations in the operating voltage.